The present invention relates to an apparatus and method for detecting defects at a gas exhaust line in a casting machine, and more particularly, to the apparatus and method for detecting clogging or perforation at the gas exhaust line in the casting machine.
Conventionally, there have been proposed various gas venting techniques for venting gas from metal molds in order to produce voidless product in casting with an injection machine such as a die-casting machine. According to the conventional techniques, suction of gas from a mold cavity is positively performed by a vacuum suction device through a gas venting device and gas exhaust line in an attempt to remove gas from the mold cavity. However, gas suction may be insufficient if the gas venting device and the gas exhaust line do not perform proper sucking operation due to their defects such as clogging. Accordingly, gas venting passage may be closed, and quality of the casted product may be degraded, and productivity may be lowered. To obviate this problem, there have also been conventionally proposed a detecting apparatus and detecting method for detecting defects such as clogging etc. in the gas venting device and the gas exhaust line.
For example, according to a Japanese Patent Application Kokai No. sho-62-137164, a spool valve is connected, through a gas exhaust line, to a gas venting device provided in the metal molds, and vacuum suction means such as a vacuum tank is connected to the spool valve through the gas exhaust line. A pressure switch is provided in the vacuum tank for detecting pressure within the suction means. The pressure switch is also connected to the spool valve through a timer and control means. When filling molten metal in the metal molds, the spool valve is opened for venting gas by means of negative pressure in the vacuum tank through the gas vent device. Inner pressure in the vacuum tank is detected by the pressure switch for checking clogging at the gas exhaust line.
If clogging occurs, the pressure in the vacuum tank, the pressure being detected by the pressure switch, does not lower to a preset level. If the pressure level does not lower to the preset level even after elapse of a predetermined time period set by the timer, the control means closes the spool valve for replacing or inspecting the gas exhaust line.
However, in the invention described in this Japanese publication, several drawbacks may be conceivable since the pressure switch is connected to the vacuum tank. For example, (1) if the vacuum tank has large internal volume, pressure dropping speed is low despite the fact that no clogging occurs, so that it would be difficult to judge whether or not the low pressure dropping speed is due to the clogging. (2) If the mold cavity has small internal volume, also, pressure drop speed in the vacuum tank is low, so that it would be difficult to distinguish the occurrence of clogging. (3) If cross-sectional area of the gas vent passage is small, it takes too much time to provide pressure drop in the vacuum tank, so that it would be difficult to judge whether or not the clogging occurs. (4) In order to perform proper detection of clogging, it is necessary to alter setting of the pressure switch in view of the reasons (1) through (3) above. (5) Even if clogging occurs, pressure drop in the vacuum tank also occurs if the gas discharge line is perforated, and thus, detection to the clogging cannot be achieved, and perforation or hole in the gas exhaust line cannot be found.
Further, according to a Japanese Utility Model Application Kokai No.62-193952, a checking vacuum tank is connected to a gas vent hole formed at a downstream of a gas vent valve of a gas vent device, and the checking vacuum tank is connected with a pressure switch. After the gas vent valve is open, the gas vent valve and the checking vacuum tank are communicated with each other, and the inner pressure of the checking vacuum tank is detected by the pressure switch for detecting opening/closing state of the gas vent valve.
However, the invention described in the Japanese Utility Model publication would provide the following problems: (1) If the checking vacuum tank has large internal volume, pressure level in the checking vacuum tank is unchanged even if the gas vent valve is open, so that judgment as to whether or not the clogging occurs or judgment of opening or closing state of the gas vent valve cannot be made. (2) If the mold cavity has small internal volume, pressure level in the checking vacuum tank is unchanged, and therefore, it is impossible to judge the state of the gas vent valve and to judge whether or not clogging occurs. (3) Due to the reason (2), pressure level must be altered with respect to each of the metal molds in order to detect the proper detection of clogging. (4) if the gas exhaust line is perforated while the gas vent valve is open and clogging occurs, the checking vacuum tank would provide the pressure change which is the same as that in case of the normal state. Thus, defect cannot be detected. (5) Proper checking vacuum tank must be required for detecting state of the gas vent valve and condition of clogging.